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Tuesday, January 17, 2006

On Pattern and Process

PZ Myers has provided an excellent summary of West-Eberhard's ideas on what evolutionary theory is currently lacking (RPM offered a population geneticist's perspective). This is a topic close to my own interests -- I too dream of an extended evolutionary synthesis, one integrating population genetics, development and phenotypic evolution. This is a major problem, which will likely occupy evolutionary biologists for decades, if not centuries, to come.

Here I would like to consider a follow up question: will current trends in evolutionary developmental biology (evo-devo) finally lead to the solution of the problems raised by West-Eberhard and others? I would like to put forward a controversial view. Although there has been spectacular progress in evo-devo, I believe that most of it will leave evolutionary theory relatively untouched. The problem is that most of current evo-devo, concentrates on what might be called pattern evo-devo (from an evolutionary perspective): the study of what the developmental mechanisms underlying a given trait are, and how these mechanisms have changed in evolution. This work has enriched our understanding of evolution immensely. However, I believe that an overhaul of evolutionary theory will require progress in the more difficult questions of process evo-devo: how do evolutionary forces, such as mutation, environmental change and natural selection, operate on developmental mechanisms, and, conversely, how does development interact with these forces to direct, bias and constrain phenotypic evolution? Many such questions have been well articulated by, among others, Gould, Arthur, Raff, West-Eberhard and the "developmental systems theorists", but progress in answering them has been slow. These questions are hard to tackle using present techniques of developmental genetics, molecular evolution and experimental evolution, but ultimately they will have to be faced if we want to usher in a "new and general theory of evolution", to borrow Gould's phrase.